Hybrid ring multicoupler for a plurality of pairs of transmitters



Sept. 13, 1966l c. E. WoLcoTT 3,273,067 HYBRID RING MULTLCOUPLER FOR A PLURALITY oF PAIRS 0F TRANSMITTERS Filed March 28, 1963 2 Sheets-Sheet 1 Arm/V5 V5 TISSMN Q3 Sept. 13, 1966 c.E.wo1 coTT HYBRID RING MULTLCOUPLER FOR A PLURALITY OF PAIRS OF TRANSMITTERS Flled March 28, 1965 2 Sheets-Sheet 2 United States Patent O 3,273,067 HYBRID RING MULTICOUPLER FOR A PLU- RALITY F PAIRS 0F TRANSMITTERS Charles E. Wolcott, El Cajon, Calif., assignor to Whittaker Corporation, a corporation of California Filed Mar. 28, 1963, Ser. No. 268,682 11 Claims. (Cl. 32E- 129) The present invention relates to means and techniques useful in coupling a plurality of high frequency sources to a common load and to a system embodying such means and techniques wherein specically a plurality of transmitters are coupled to a common antenna system.

The systems disclosed herein involve the use of one or more hybrid rings to cou-ple a plurality of radio transmitters operating within a 2-30 megacycle frequency band to a single antenna.

Multicoupling functions are performed using low loss, air dielectric, coaxial transmission lines at these relatively low frequencies.

There has long existed a need for a multicou-pling system which uses only a single antenna with a plurality of transmitters operating in the frequency range of 2-30 megacycles .per second and feeding such single antenna. Prior arrangements operating in this frequency band used lumped constant reactive elements arranged into -lter or tuned resonant circuitry, thereby imposing certain limitations on the system such as, for example, permissible bandwidth, power-handling capacity, and number of transmitters which may be coupled to a single antenna.

An important feature of the present invention involves the concept of using hybrid rings operating in conjunction with coaxial lines or other elem-ents having distributed impedances at these relatively low frequencies in the 2-30 megacycle range. I-Ieretofore, the hybrid ring has been employed lprimarily as `a mixer at microwave frequencies in radar `and related systems and has also been used to a limited extent to combine power in television transmitting systems operating in the very high or ultrahigh frequency range.

It is therefore a general object of the present invention to provide improved means and techniques for eiciently coupling a plurality of transmitters to a sing-le antenna without substantially any transmitter interaction or power loss.

A specific object of the present invention is to provide a system of this character in which two adjacent channel operating transmitters are eiciently coupled t-o a single antenna without the necessity of maintaining a fixed percentage of frequency separation 'between the two channels.

Another specific object of the present invention is to -provide a system of this character which does not require tuning adjustments to be made during small adjacent channel frequency changes.

Another specic object of the present invention is to provide a system of this character which allows the carrier frequency of any transmitter of the system to be adjusted without having to readjust the associated adjacent channel transmitters.

Another specific object lof the present invention is to provide a system of this character in which the coupling system imposes a small insertion loss and minimizes the possibility of failure due to voltage breakdown.

Another specific object of the present invention is to provide a system of this character which uses hybrid rings ICC with suitable impedance matching between transmitters and the common antenna.

Another specic object of the present invention is to provide a system of this character which provides a low voltage standing wave ratio throughout the entire operating band.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. This invention itself, both as to its organization and manner of operation, together with further objects and advantages thereof, may be best understood by reference to the following description taken in connection with the accompanying drawings in which:

FIGURE 1 illustrates a system embodying features of the present invention;

FIGURE 2 illustrates a form of hybrid ring which may be incorporated in the systems disclosed herein;

FIGURE 3 shows a portion of a hybrid ring for achieving a phase reversal whereby the four arms of the ring may be equally spaced degrees apart as shown in FIG- URES 1 and 4 instead of as in FIGURE 2;

FIGURE 4 serves as an illustration of another system embodying features of the present invention;

FIGURE 5 represents the electrical equivalent circuit of the arrangement shown in FIGURE 3 at the normal operating frequency of the hybrid ring of which such arrangement forms a part.

Each of the arrangements described herein uses one or more six quarter-wavelength coaxial hybrid rings exemplied in FIGURE 2 and having the arms l, 2, 3, and 4 extending from the ring .portion 5. As dimensioned in FIGURE 2, the arm 1 is spaced one-quarter of a wavelength from arm 2 and three-quarters of a wavelength from arm 3; arm 2 is spaced a quarter wavelength distance from arm 4; and arm 4 is spaced a quarter wavelength distance from arm 3. Thus, at the operating frequency there is no direct coupling between larms 1 and 4 or between arms 2 and 3 since the spacing in each case is onehalf of one wavelength. This is due to the electrical length of the ring elements being such that if a frequency source is coupled to arm 1, the electrical length to arm 4 around the side containing arm 3 is one wavelength, and the electrical length to yarm 4 around the side containing arm 2 is one-half wavelength, thus resulting in wave cancellation at the junction of arm 4. Thus, both arm 1 and arm 4 are isolated from each other when simultaneously supplied with voltages at a similar frequency. A voltage source SA is coupled to arm 1 and a voltage source SB is coupled to arm 4, and when the frequency of these two sources is identical, there is a theoretical maximum isolation between arms 1 and 4. This isolating characteristic of the hybrid ring is used to overcome the problem of adjacent channel frequency separation which prevails in existing multicoupler systems. The present multicoupling system employing a hybrid ring combines the outputs of two transmitters to -allow the transmitters to operate either at the same frequency or at slightly different frequencies under power conditions without danger of transmitter burnout.

It is preferred that the three-quarter-wavelength element of the six quarter-wave ring shown in FIGURE 2 be -substituted by 'a portion having a physical length of one quarter-wavelength and this is accomplished by a reversal in phase in such element, such reversal in phase being accomplished, for example, by the arrangement shown in FIGURE 3 which is described later. By thus providing a 3 phase reversal, the three quarter-wavelength dimension then actually has a quarter-wavelength physical length and in such case, the arms 1, 2, 3 and 4 are equally spaced physically around the ring with a 90-degree angular separation between the same as illustrated in FIGURES l and 4.

Various means may be used to ac-complish such phase reversal in the three quarter-wavelength arm and, as shown in FIGURE 3, this is accomplished by the use of a pair of aluminum discs 10 and 11 to which opposite ends of a coil 12 are connected. These discs 10 and 11 are connected also respectively Ito ends 6A and 6B of the interrupted inner conductor 6 (FIGURE 2) of the coaxial ring 5. The discs 10 and 11 and coil 12 are within a cylindrical housing 14 of metal which is joined to the outer metal tubular portion of ring and insulation 15 surrounding the discs 10, 11 and coil 12 insulates these elements from the outer metal portion of the ring. This construction thus preserves the coaxiality of the inner and outer metal portions of the ring and results in the three quarter-wavelength arm to have a physi-cal length of one quarter-wavelength but yet an electrical length of three quarter-wavelengths.

The arms 1, 2, 3, and 4 in FIGURE 2 are correspondingly numbered in FIGURES l and 4. It will be seen that in FIGURE l there are provided eight six-quarter electrical wavelength rings 5, each having a different nominal operating frequency with two pairs of four rings each. Thus, a rst pair comprises a ZO-megacycle, -megacycle, 5megacycle, and 2.5-megacycle rings and the other pair comprises 28megacycle, 14-megacycle, 7-megacycle, and 3.5-megacycle rings.

The number 1 and number 4 arms of each ring are, as shown, connected through a corresponding ilter to a corresponding high-frequency source, i.e. transmitter, which is either unmodulated or modulated in accordance with well known techniques. Thus, using the -megacycle ring as an example, its number 1 arm is coupled to the transmitter 20 through a lter -circui-t 21 and the number 4 arm is coupled to the transmitter 24 through lter circuit 25. The transmitter 20 is adjusted to a frequency within the range of 16.5 to 23.5 megacycles and the other transmitter 24 may be adjusted to a frequency in the same `range as indicated in the drawings. This frequency range of operation, as indicated also for the other transmitters, has a midfrequency which corresponds to the nominal frequency of the hybrid ring to which such transmitters are coupled through arms 1 and 4. These connections or couplings to the hybrid rings are, of course, through coaxial connections.

The number 3 arms of each of the 20, 10, 5, and 2.5- megacycle rings .are coupled to spaced points 30, 31, 32, and 33, lrespectively, along a transmission line 35 which is shorted at one of its ends 36 and which includes the adjustable sections 35A, 35B, 35C, and 35D, these `sections being adjustable to achieve the electrical spacings of such arms 3 to the shorted end 36 of the transmission line. Likewis'e, the number 2 arms of the 20, 10, 5, and 2.5- megacycle rings are connected respectively to points 40, 41, 42, and 43 along the transmission line 45 which has one of its ends shorted at 46 and which comprises adjustable lengths 45A, 45B, 45C, and 45D to obtain the quarter-wavelength spacings indicated in the upper portion of FIGURE 1. The transmission lines 35 and 45 have their other ends coupled to the input terminals 38 and 48, respectively, of an antenna system 50 mounted on a grounded mast 51.

The other 28, 14, 7, and 3.5-megacycle rings are similarly coupled with the number 1 and number 4 arms of each being coupled to a separate transmitter and with the number 2 and number 3 arms of each being coup-led to spaced points along the transmission lines 80 and 70, respectively. One end of each of the lines 70 and 80 is shorted [at 71 and 81, respective-ly, and the other ends of such lines 70 and 80 are coupled respectively to the antenna input terminals 72 and 82. The transmission line 70 comprises adjustable sections 70A, 70B, 70C, and 70D; and the transmission line comprises the adjustable sections 80A, 80B, 80C, and 80D.

The arms number 3 lof each of the 20, l0, 5, and 2.5- megacycle rings are spaced an electrical length from the shorted transmission line end 36 a distance equal to one quarter-wavelength of the nominal frequency of the corresponding ring; and likewise, the number 2 arms of each of these rings are spaced an electrical length from the shorted transmission line end 46 a distance equal to onequarter of a wavelength of the 4frequency of the corresponding ring, this being indicated at the upper portion of FIGURE 1. For example, the arm 3 of the 20-megacycle ring is electrically spaced from the shorted end 36 a distance of one quarter-wavelength at 20 megacycles; the arm 3 of the IO-megacycle ring is spaced one quarter of a wavelength at 10 megacycles from the same shorted end 36; and likewise, the arm 2 of the 20-megacycle ring is spaced electrically a distance equal to one-quarter of a Wavelength at 20 megacycles from the shorted end 46 and the arm 2 of the IO-megacycle ring is spaced electrically a distance from such shorted end 46 equal to one quarter of a wavelength at 10 megacycles. This corresponding relationship is also true with respect to the 28, 14, 7, and 3.5-megacycle rings. For example, the number 2 and number 3 arms of the 28-megacycle rings are spaced electrically one quarter of a wavelength from the shorted ends 81 and 71, respectively, at the frequency of 28 megacycles; and the arms 2 and 3 of the l4-megacycle ring are spaced electrically from the shorted ends 81 and 71 a distance equal to one-quarter of a Wavelength at 14 megacycles. Thus, each of the rings is coupled to a transmission line one qua-rter of a wavelength from the shorted end of the line with the result that each transmitter sees a high impedance when looking backward down the line towards the corresponding shorted line and sees a frequency multiple of one-half of a wavelength when looking up the line towards the antenna. It is recalled that transmission line theory dictates that a quarterwavelength line inverts the independence at the end of the line and that half-wavelength line repeats the impedance at the end of such half-wave line.

Thus, wave transmission from the hybrid rings is forwardly to the antenna system without substantially any interaction between the individual transmitters which are effectively isolated one from the other with the transmission lines providing isolation between rings land the ring itself isolating the particular pair of transmitters coupled thereto through the arms 1 and 4.

In the modification shown in FIGURE 4, the 20- rnegacycle, 10-megacycle, 5megacycle, and 2.5-megacycle rings are cascaded and this figure serves also to illustrate the manner in which the other four 28, 14, 7, and 3.5-megacycle hybrid rings are cascaded and interconnected to the same segmented antenna as in FIGURE 1. Here again, as in IFIGURE 1, a pair of transmitters, operating within the Afrequency range of that particular ring, is coupled to such ring through arms 1 and 4. The highest frequency ring has its number 2 arm coupled to the number 3 arm of the next lowest frequency ring, with the number 3 arm of the highest frequency ring being coupled to the antenna terminal 38 and with the arm 2 of the lowest frequency ring being coupled to the antenna terminal 82. In this case the ring isolates those two sources which are connected thereto through 'arms 1 and 4 and also the quarter-wavelength sections of such ring provide isolation of these same transmitters from transmitters connected to the other rings through corresponding arms 1 and 4.

Preferably each source is connected to its corresponding ring through an impedance-matching network and a tunedy circuit which is `tuned to the same frequency as that transmitter which is coupled by such tuned circuit. Thus, for example, the transmitter 90, adjusted to operate at a frequency within a range of 16.5 to 23.5 megacycles, is coupled through transmission line 91, having an impedance of 70 ohms, to a tapped coil 92. The sheath of the line 91 is connected to the grounded end of coil 92 and the inner conductor of the line is connected to Ia tap 94 on coil 92. A second tap 95 on the coil is connected through a series resonant .circuit comprising adjustable coil 97 and adjustable capacitor 98 to arm 4. A capacitor 99 is connected between ground `and the tap 95. The other transmitters are likewise connected to corresponding arms of corresponding hybrid rings yas shown in FIGURE 4.

This arrangement provides improved impedance matching between a frequency source and the corresponding hybrid ring input port or arm. The impedance-matching network comprising the tapped coil 92 allows greater flexibility in performance. Two primary benefits are obtained through the use of such matching network. First, the most important is the impedance match condition achieved between a wide range of transmitter output impedances and the 70ohm ring port impedance. Secondly, the network described provides frequency selectivity which is adjustable to only the passive frequency, and this presents a high impedance to any other frequency source which looks backward on the line connected to the ring port. Thus, preferably impedance matching and an additional isolation characteristic is achieved prior to application of the transmitter input to the input of the ring.

In considering impedance matching to a ring, it should be noted that the impedance looking into a junction from a side arm of the ring is the sum of the impedances seen looking -both ways into the ring junction. The characteristic impedance of the ring, therefore, is generally greater in value than that of the side arm 4by a factor of the square root of two. It is desirable, from a manu-facturing point of View, for both the ring and side arm coaxial lines extending therefrom to have the same outer conductor diameters and the impedance values may be selected through choice of the diameter of the coaxial center conductor. The ratio between outer and inner diameters of the ring conductors may, for example, be 3.57 although it is understood that this ratio may be changed to achieve different impedance conditions.

Preferably, for purposes of flexibility and versatility in operation and adjustment, the rings and branch lines are made so as to be adjustable in length using so-called line-stretchers involving a so-called trombone construc tion involving sliding fits between sections of the inner and outer conductors. Preferably, such trombone construction allows a twenty percent change in physical length to allow optimum tuning under all possible operating conditions.

Preferably, the particular type of matching network specifically illustrated in FIGURE 4 is incorporated in the system shown in FIGURE 1.

In the cascade arrangement of hybrid rings shown in FIGURE 4, adjacent ones of the rings are interconnected by o-ne-half wavelength sections as indicated for the flow of energy therebetween, it being noted that the halfwavelength lines between the arms or legs 2 and 3 are one-half wavelength long at the higher 4frequency of the two interconnected rings. Thus, for example, the number 2 and number 3 arms of the 20- and lO-megacycle rings, respectively, are interconnected by a line which is one-half wavelength at megacycles. While, as discussed above in connection with FIGURE 2, there is isolation between terminals 2 and 3 of the same ring and at the nominal frequency of that particular ring, this is not the case when frequencies other than the nominal frequency of that particular ring is considered, this being so due to the fact that :the pi phase section in each three quarter-wavelength arm provides a phase shift of 180 only at the particular nominal frequency of that hybrid ring in which the pi section under consideration is located. This will be seen from FIGURES 3 and 5 wherein FIGURE 3 illustrates the physical construction of the pi phase section of the three-quarter arm and FIGURE 5 illustrates the equivalent circuit of the construction shown in FIGURE 3 which is the equivalent circuit only at the particular ring =frequency. The equivalent circuit shown in FIGURE 5 is illustrated as having a pi configuration with a series inductance arm and -a pair of shunt-connected capacitors 141 and 142 shunting respectively what may be termed the input and output terminals of the network; and additionally, due to the distributed capacitance `of the coil 12 of FIGURE 3, there is present an additional capacitance 143 represented as having one `of its terminals connected to the midpoint of inductance 140, i.e. of coil 12. This construction of the pi section shown in FIGURE 3, with its placement being indicated by the Greek letter pi in FIGURE 4, allows, for example, energy from the IO-megacycle ring to be transferred from the number 2 and number 3 arms of the 20-megacycle ring and thence to the antenna terminal 38. Likewise, energy from both transmitters coupled to the `arms 1l and 4, respectively, of the 5-megacycle ring is transferred to the antenna terminals 3S and 82 through the 2.5-megacycle, lO-megacycle, and 20- megacycle rings. This is so since the pi sections in the 2.5-megacycle, 10-megacycle, and 20-megacycle rings do not impose a -degree phase reversal of energy at 5 megacycles.

The antenna used in either the system shown in FIG- URE l or FIGURE 3 is preferably of the sectionalized type which is suitably terminated such that the voltage standing wave ratio does not exceed 3 to l over the 2-30 megacycle range. Preferably one antenna is stacked directly on top of another to avoid the configuration of a spaced array. When, as is preferred, the multicoupling system comprises adjustable line lengths, the phase is controllable at any operating frequency such that the radiation angle of the sectioualized antenna may be 'adjusted and controlled at all frequencies of operation.

Preferably, the antenna combines the characteristics of the cage and discone antennas, with the lower frequency part of the 2-30 megacycle band division being radiated by the cage portion of the antenna and the high frequency part of the division by the discone. Thus, as illustrated, the antenna consists of two :cage-discone antennas .stacked one above the other and with one inverted, The two section cages are used for the 2-8 megacycle part of the band the two section conic portions are used for the 8-30 megacycle part of the band.

The arrangements disclosed herein are thus useful for combining the output power of up to sixteen, 5,000-watt CW or 10,000-watt modulated radio transmitters within a 2-30 megacycle frequency band. This is done by providing symmetrically fed circuits having a single plane of `symmetry which passes through the two input ports or arms. If one transmitter is retuned for proper loading, or additional frequency adjustment, instability transients have little or no effect on other transmitters, thereby eliminating the necessity of a readjustment of all transmitters as in prior art arrangements wherein the loading and tuning is complicated by the introduction of transients that necessitate .a complex retuning and readjustment procedure. By isolating one transmitter from other transmitters, loading and tuning of la particular transmitter may be accomplished on an individual basis, a highly desirable condition.

It Will thus be seen that the multicoupling band combiner consists of eight Lcoaxial line hybrid rings grouped into two independent cascade series interconnected with coaxial intercostal lines. The conventional three-quarter pi phase shifter and a quarter-wavelength section of co- Number l Cascade Number 2 Cascade 2. MC 3. 5 MC 5. 0 MC 7. 0 MC 10. 0 MC 14. 0 MC 20. 0 MC 28. 0 MC The two input ports of each hybrid ring are isolated approximately 42 db from each other. Thus, the 15% channel frequency separation normally mandatory with conventional multicouplers does not apply to the hybrid ring multicoupler. The hybrid ring system, due to its close frequency isolation characteristics, overcomes the problems of frequency pulling, signal priming, mutual synchronization and the transmitter burn-out hazards of former multicoupler systems. Maximum isolation is achieved when two adjacent channel transmitters are tuned to the same frequency.

The sixteen multicoupled transmit channels are grouped in pairs which correspond to the two input ports of each of the eight hybrid rings. Both ports of each hybrid ring have the same bandwidth and cover the same channel frequencies. The subdivision, therefore, provides the 'following channel frequencies:

Nominal Ring Channel Channel Cascade Number Frequency in Number Frequencies Megacyeles in Mcgacycles Each of the sixteen transmitter input channels contains a channel matching filter. This matching lter functions to match the SO-ohm hybrid port input impedance betiween 2S to 75 ohms, such that, the transmitter eiiectively sees la resistive load. The matching iilter contains a series resonant circuit which is adjusted by a single control to the frequency being transmitted. The yolf-frequency isolation of this series resonant circuit plus the inherent powersplit characteristics of the hybrid provides a minimum 42 db isolation from other hybrid rings in the cascade series. The frequency separation of hybrids in the cascade is noted to be such that isolation is always achieved between all cascade channels. Filter isolation adds to hybrid isolation when the pair of hybride inputs are yfrequency separated.

Each hybrid ring cascade has tJwo 50-ohm coaxial output lines. This is due to the poiwer split character orf the hybrid. Since the multicoupler unit is composed of two ring cascades, four 50-ohm coaxial outputs must be accepted by the antenna system used for maximum eiciency of operation. A compatible antenna is described herein; hoiwever, other antennas such as back-to-back r-hombics for two-direction transmission may also be used.

A counter dial control may be provided for each of the sixteen channel matching lters. These tuning controls can be made autotune if desired by installing a line phase discriminator, a transistor amplifier, and a size 18 servo motor for each channel. These components are commercially available.

Multicoupler performance monitoring may be provided by channel current metering and VSWR, i.e. voltage standing wave ratio, measurement at each hybrid. The multicoupler unit is designed to work into a maximum load VSWR of 3:1 at maximum power rating. Components are conservatively rated for forty kilowatt channel operation if the number of channels in use are limited. The coaxial lines used are two-inch outer conductor SO-ohm and -ohm sizes. Line stretches are employed which are capable of changing all line lengths twenty feet in each one hundred feet. These line stretchers may be adjusted to frequency settings and output line phasings during factory assembly checkout `and remain at this setting.

It is noted that only high Q elements are used for all multicoupling and band combining circuitry. Since the hybrid rings and intercostal lines are constructed of lowloss air dielectric coaxial transmisison lines, the eiciency is very high in the 2-30 megacycle communication bands.

The sectionalized antenna consists of two discage antennas stacked one above 'the other with the top section inverted.

The discage configuration is that of two conical sections joined base-to-base such that theI lower cone is inlverted. The two joined cones constitute Ithe cage antenna which is used for the 2-8 megacycle band. The single cone at the top of the antenna is used for the 8-30 megacycle band. The discage has two feed points which are the top and bottom.

The impedance characteristics of both the cage and cone portions of the antenna are good. The VSWR of both, covering the 2-30 megacycle band, is 3:1 or better, referred to 50 ohms. No matching transformers are required tor either section. There is no measureable intera'ction in the cone from the cage portion. The two stacked discage antennas form an omnidirectional sectionalized antenna which is 126 `feet high and 34 feet, 2 inches at the maximum cage diameter. The active elements of the antenna are constructed of phosphor-bronze cable. The Iground system uses sixty #8 copper radials feet long. The sectionalized discage antenna requires four 50-ohm unbalanced feeder-lines ifor 'full bandwidth performance. Phasing of the feeder-lines to control antenna radiation angle is preset by the line stretchers for each hybrid nominal frequency in .the multicoupler unit.

While the particular embodiments of the present invention have been shown and, describe-d, it 'will be obvious to those skilled in the art that changes and modiiications may be made without departing [from this invention in its broader aspects and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

I claim:

1. In a system of the character described wherein it is desired to couple a plurality of transmitters to a single antenna, a riirst hybrid ring, a second 4hybrid ring, a rst pa-ir of transmitters each operating at a frequency somewhat different than a rst nominal frequency and each being coupled to said iirst ring, a second pair of transmitters each operating at a Ifrequency different than a second nominal frequency and each being coupled to said second ring, a transmitting antenna, and means coupling each of said rings to said antenna, said coupling means including connections between said tirst and second rings, said connections having an electrical length substantially equal to one-half of the wavelength of one of said nominal frequencies for isolating said irst ring from said second ring.

2. A system as set forth in claim 1 in ywhich said coupling means comprises a transmission line having a shorted end, and said first and second hybrid rings are coupled to said transmission at points thereon one quarter of a wavelength of the operating frequency of the corresponding ring .from said shorted end.

3. A system as set forth in claim 1 in which said coupling means from one hybrid ring to said antenna includes the other hybrid ring.

4. A system as set forth in claim 1 in which at least one of asid transmitters is coupled to its corresponding ring througha transmission line having a grounded sheath and an inner conductor, a coil having one terminal grounded and a first tap thereon connected to said conductor, a second tap on said coil being connected to an arm of said `ring through a series resonant circuit resonant to the frequency of said one transmitter.

5. In a coupling system of the character described, a first six quarter-Wavelength hybrid ring at a 4first nominal frequency, a second six quarter wavelength hybrid ring at a second nominal frequency, each ring having two pairs of conjugate arms with each arm of a pair being isolated from the other arm of the same pair, a first pair of transrnitters coupled -respectively to said first ring lthrough different arms of one conjugate pair thereof, a second pair o-f transmitters coupled respectively to said second ring through different arms of one conjugate pair thereof, an antenna, said antenna being coupled Ito the other pair of conjugate ar-ms of each ring through connections having an electrical length substantially equal -to one-half of the wavelength orf one of said nominal frequencies for isolating said first ring from said second ring.

`6. A system as set forth in claim 5 including a pair of transmission lines each having a shorted end and each having its other end coupled to an antenna, said other pair of conjugate arms of the first ring being coupled to corresponding opposite ones of said transmission lines one quarter of ya wavelength of the nominal yfrequency of said -first ring from the shorted ends thereof, said other pair of conjugate arms of the second ring being coupled to corresponding opposite ones of said transmission lines one quarter of a wavelength of the nominal frequency of said second ring from the shorted ends thereof.

7. A system as set forth in claim 5 in lwhich one of said other pair of conjugate arms of sai-d first ring is coupled to one of said other pair of conjugate arms orf said second ring through a transmission line having one half wavelength at the nominal frequency orf said second ring, and said second ring havin-g a frequency dependent Ithree quarter Wavelength section containing lumped reactances for preventing said other lpair of conjugate arms of said second ring from being conjugate at frequencies substantially removed from the nominal frequency of said second ring.

`8. A system as set forth in claim 6 in which the nominal frequency of one .ring is a multiple of two of the nominal frequency of the other ring.

9. A system as set forth in claim 6 in which said rings, transmitters and transmission lines are duplicated to pro'vide a second pair o|f transmission lines, and said antenna has a pair of sections each with a pair of terminals, each pair of said terminals being connected between transmission lines of different pairs thereof.

10. A system as set forth in claim 9 in which the first and second hybrid rings have a nominal lfrequency differing yfrom each other by a factor of two wi-th the nominal frequency of said duplicated hybrid rings differing from the nominal frequency of said lrst and second rings by a factor of 1.4.

11. A system as set forth in claim 9 in which said antenna comprises two cage-discone antenna sections.

References Cited by the Examiner UNITED STATES PATENTS 1,934,602 1l/1933 Gilman 343-208 2,445,895 7/ 1948 Tyrrell S33-11 2,543,973 3/ 1951 Jensen 333-11 2,602,887 7/1952 Brown 325-157 3,001,194 9/1961 Leppert 343--896 OTHER REFERENCES Pages 121-127, January 1959, Cline and Schiffman. Tuna-ble Passive Multicouplers Employing Minimum- Loss Filters. yIn IRE Transactions on Microwave Theory and Techniques.

Pages 112-116, September 1951, Firestone. Multiplexing of Klystron Oscillators. Electronics. Vol. 24, No. 9.

DAVID G. REDINBAUGH, Primary Examiner.

B. V. SAFOUREK, Assistant Examiner, 

1. IN A SYSTEM OF THE CHARACTER DESCRIBED WHEREIN IT IS DESCRIBED TO COUPLE A PLURALITY OF TRANSMITTERS TO A SINGLE ANTENNA, A FIRST HYBRID RING, A SECCOND HYBRID RING, A FIRST PAIR OF TRANSMITTERS EACH OPERATING AT A FREQUENCY SOMEWHAT DIFFERENT THAN A FIRST NOMINA FREQUENCY AND EACH BEING COUPLED TO SAID FIRST RING, A SECOND PAIR OF TRANSMITTERS EACH OPERATING AT A FREQUENCY DIFFERENT THAN A SECOND NOMINAL FREQUENCY AND EACH BEING COUPLED TO SAID SECOND RING, A TRANSMITTING ANTENNA, AND MEANS COUPLING EACH OF SAID RINGS TO SAID ANTENNA, SAID COUPLING MEANS INCLUDING CONNECTIONS BETWEEN SAID FIRST AND SECOND RINGS, SAID CONNECTIONS HAVING AN ELECTRICAL LENGTH SUBSTANTIALLY EQUAL TO ONE-HALF OF THE WAVELENGTH OF ONE OF SAID NOMINAL FREQUENCIES FOR ISOLATING SAID FIRST RING FROM SAID SECOND RING. 